It is probable in most swimming pool facilities that the swimming pool water is recirculated by a motor driven pump so that the pool water can be continuously filtered and in addition pass through a suitable heater so as to maintain the water substantially free of debris and at a selected temperature.
Swimming pool water can be kept substantially free from bacteria, viruses and algae by the addition of certain selected chemical compounds, for example by introducing liquid or gaseous chlorine or sodium hypochlorite or calcium hypochlorite either in its crystalline form or in solution in a quantity sufficient under given conditions to yield a level of free chlorine which will at least inhibit the growth of or destroy those contaminants.
If free chlorine is present in an amount of approximately 1.5 parts per million in water maintained at a temperature of the order of 80.degree. fahrenheit and of a pH of approximately 7.6 to 7.8 then optimum conditions prevail in which bacteria, viruses and algae likely will be destroyed or their growth severely inhibited.
The required amount of selected chemicals to provide adequate free chlorine concentration will increase with temperature. Also such amount will be affected by the character of the pool water itself, for example its degree of hardness and whether the pool is subjected to heavy or light use.
In some cases higher levels of free chlorine may be warranted as a precautionary measure especially where the pool is under heavy use or where alage growth flourishes. In some jurisdictions regulations governing the operation of public or commercial pools prescribe higher levels of available free chlorine than would normally be necessary.
The selected chemical additives can be introduced on the pressure side of the associated pumping system in installations where pool water is recirculated. Natural forces of diffusion and convection also work under recirculation to the end that substantially uniform distribution of the chemical additive is achieved in a relatively short interval of time after introduction.
The pH of pool water is also subject to variation depending in part upon the character of the water itself. It has become common practice to control the pH by the introduction of still other chemicals to establish the aforementioned range of 7.6 to 7.8 approximately, which chemicals will also be disseminated throughout the pool by the recirculation pump and associated natural forces. The pH range so established by known methods tends to minimize the effect of the combined chlorine or chloramines which in certain concentrations irritate human tissue.
Following introduction and distribution of the inhibiting and controlling chemicals, their effective concentrations diminish or shift through reactions with contaminants by decomposition and also through exposure to sunlight. Consequently, original levels must be restored from time to time by the addition of still more additives.
Procedures and schedules have been developed to properly test pool water at intervals for free chlorine concentration and to determine the pH with the additives then weighed out in sufficient quantity and physically introduced at specified points at the pool periphery.
In other cases the chemical additives are introduced in solution of known strength supplied by commercial sources with the requisite volumes of liquids added to the pool water at specified points at the pool periphery or through an appropriate conduit leading to the pressure side of the recirculation pump discharging the water back into the pool.
Procedures involving the testing of pool water for determining free chlorine concentration and pH followed by the addition of measured quantities of the inhibiting and controlling chemicals calculated upon specific test results taken before the addition may shift those concentrations in pool water beyond acceptable limits for either comfort or safety and even cause conditions which tend to support the growth of the contaminants rather than suppress them.
With this invention the degree of control over the variables encountered with such recirculated pool water is substantially increased yielding a body of water fit for use at all stages of the application of the method.